Banding sleeves on hardware is a very common technique from the standpoint of design, so that today there are many joints in which some sliding sleeves are fitted over some banded sleeves these in turn embedded in holes in the hardware itself, being adjusted on the other side on the sliding sleeves a bolt or similar axially fixed, through which all of the hardware assembly is linked to another element. In all cases, all of the sleeves shall be adjusted with a predetermined and perfectly calculated torque.
Thus, in principle banded sleeves must remain fixed throughout the life of the joint, but in reality we can find cases where these sleeves “migrate” and leave their housing in the hardware. This migration causes a loss of strength in the hardware lug, and may even lead to its failure with the serious consequences that this would imply.
Hence the importance of knowing throughout the life of the aircraft if these sleeves are well installed or, if on the contrary, have lost torque and have migrated.
The way to see in service, during maintenance, if these sleeves migrate or not is through a detailed visual inspection of the area. Also, in some cases if the access allows us, we can measure with a gauge the diameter of the visible part of the sleeve and check if it is the diameter of the banded sleeve or it is the diameter of the sliding sleeve.
These methods are based on the fact that there is good access to the area in question and that simply with a visual inspection of the area or with a gauge we can determine whether the cap has migrated or not.
In contrast, when the access to the area to be inspected is not good, the difficulty of a visual inspection that can be 100% reliable decreases. Moreover, even if we get access to introduce a small ruler and even if we could measure, for example, a preset distance, which would allows us to know if there is migration, as soon as we were not able to obtain, when measuring, a good perpendicularity on the edge of a lug, that measurement could be distorted. If we add that the banded sleeve may have a very small thickness, the deviations of the perpendicular of only a few degrees can make us believe that the banded sleeve has not migrated when it has, in fact, migrated.